1. Field of the Invention
The present invention relates to a keyboard unit for an electronic musical instrument.
2. Prior Art
Conventionally, the keyboard unit of the electronic musical instrument provides a key switch below the lower-side portion of each of the keys. This key switch produces a key-on signal when a key is depressed. When depressing the key, the key is depressed down in a vertical direction by the predetermined stroke. Hereinafter, such stroke will be denoted to as a key-depression stroke. In the Vicinity of the end zone of this key-depression stroke, there is provided a pressure sensor, by which the musical tone control is performed with respect to the after-touch range of the musical tone. For example, when imparting the vibrato effect to the musical tone, the key is slightly vibrated after the key is depressed down by the key-depression stroke. At this time, the vibrating motion of the key causes the variation of the pressure applied to the key, which is sensed by the pressure sensor so as to perform the frequency modulation on the musical tone so that the tone pitch will be altered regularly.
In the conventional keyboard unit, the above-mentioned musical tone control (e.g., vibrato effect) is performed on the musical tone with respect to the after-touch range only after the key-stroke range is ended. This provide a limitation to the performability of the keyboard. In other words, the control range for the musical tone cannot be sufficiently enlarged, which causes a drawback in that the sufficient performability for the musical tones cannot be obtained.
When observing the structure of the keyboard, in order to slightly alter the tone pitch designated by the key-on signal corresponding to the depressed key, the conventional electronic musical instrument is designed to arrange the keys such that each of the keys can be moved in a lateral direction of the keys to be disposed. In response to the lateral-deviating motion of the key to be depressed, the tone pitch is controlled.
In the keyboard unit providing the above-mentioned structure, the key-guide unit in which the keys are arranged is stored in and supported by the key-frame unit. This key-frame unit, as a whole, is attached to the keyboard instrument such that it can freely move. On the basis of the result of the detection of the motion of the key-frame unit, the tone pitch is controlled.
As described above, the key-frame unit as a whole is moved against the keyboard instrument so as to detect the movement of the key-frame unit. Therefore, it is necessary to move the key-frame unit as a whole in a lateral direction by the relatively large physical power. In order to move the key-frame unit in a lateral direction, the whole structure of the keyboard unit must be enlarged and complicated.
Since the key-frame unit provides some printed circuit boards in which several kinds of electronic circuits are fabricated, these printed circuit boards must be moved when the key-frame unit is moved. Due to the repeating movements of the key-frame unit, the electronic circuits and connection cables car be damaged soon, which deteriorates the reliability and durability of the electronic circuits.